Field of the Invention
The present disclosure relates to a toner, a toner stored unit, an image forming apparatus, and a method for producing a toner.
Description of the Related Art
In recent years, there has been a need for toners to have a small particle diameter and hot offset resistance for improvement of output image qualities, to have low-temperature fixability for energy-saving, and to have heat-resistant storage stability sufficient for enduring high temperatures and high humidities during storage and transportation after production. Particularly, improvement of low-temperature fixability matters significantly because power consumption during fixing accounts for large part of power consumption in the image forming process.
Hitherto, toners produced by a kneading/pulverizing method have been used. However, the toners produced by the kneading/pulverizing method have problems: the toners cannot realize sufficient output image qualities because it is difficult to make the toners small in particle diameter and the toners have irregular shapes and broad particle diameter distributions; and the toners need a high fixing energy. When waxes (release agents) are added in the toners to be produced by the kneading/pulverizing method in order to improve fixability, the toners are torn at wax interfaces during pulverization, to have much wax on the toner surfaces. This facilitates the releasing effect, but on the other hand, makes adhesion (filming) of the toners on carriers, photoconductors, and blades more likely to occur. This is problematic because the total performance of the toners cannot be satisfactory.
Hence, in order to overcome the problems of the kneading/pulverizing method, there has been proposed a toner producing method based on a polymerization method. Toners to be produced by the polymerization method can be made small in particle diameter easily, have sharper particle size distributions than the toners produced by the kneading/pulverizing method, and can have releasing agents enclosed inside. As a toner producing method based on the polymerization method and aiming for improvement of low-temperature fixability and improvement of hot offset resistance, there is proposed a method of producing a toner from an elongation reaction product of a urethane-modified polyester serving as a toner binder (see, for example, Japanese Patent No. 3762075 (Patent document 1)).
Further, in order to improve low-temperature fixability, it is known to introduce a crystalline resin having a sharp melting property. That is, with crystallinity, the crystalline resin can maintain heat-resistant storage stability until immediately before the melting start temperature, but at the melting start temperature, the crystalline resin undergoes a sharp viscosity drop (sharp melting property) and fixes. Therefore, the crystalline resin makes it possible to design a toner having both of a good heat-resistant storage stability and a good low-temperature fixability. Furthermore, in order to improve low-temperature fixability and maintain toner qualities in a high-temperature, high-humidity environment, there are disclosed methods for making a crystalline resin small in particle diameter. There is disclosed a method of dissolving a crystalline resin together with a non-crystalline resin in an organic solvent by heating in order to obtain a stable dispersion liquid of the crystalline resin having a small particle diameter, cooling the obtained solution to recrystallize the crystalline resin, and making the resultant into particles with a mechanical pulverizer (see, for example, Japanese Patent No. 5467505 (Patent document 2)). There are disclosed some more methods for making a crystalline resin small in particle diameter in a dispersion liquid (see, for example, Japanese Patent No. 5779902 (Patent document 3), Japanese Unexamined Patent Application Publication No. 2005-107387 (Patent document 4), and Japanese Unexamined Patent Application Publication No. 2005-015589 (Patent document 5)).
Further, there is disclosed a toner in which a dispersion particle diameter of a crystalline resin is small and the ratio between the longer axis and shorter axis of the crystalline resin is from 2 through 15 (see, for example, Japanese Unexamined Patent Application Publication No. 2015-72445 (Patent document 6)).
Furthermore, there is disclosed a toner in which a ratio (Dv/Dn) of a volume average diameter Dv of a crystalline polyester resin to a number average diameter Dn of the crystalline polyester resin is from 1.0 through 2.25 in order to make the dispersion particle diameter of the crystalline polyester resin uniform (see, for example, Japanese Unexamined Patent Application Publication No. 2015-52712 (Patent document 7)).